This invention relates to pneumatic powered chain or cable hoists or the like such as are shown for example in U.S. Pat. No. 3,125,200.
Heretofore, such hoists have been noted for being extremely "noisy" in that their air exhausts are notably both shrill and staccato because of the thermodynamic limitations which are imposed upon typical type positive displacement motors resulting in incomplete air expansion cycles of operation, whereby the air exhausts from such motors are inherently in the form of rapidly expanding high pressure bursts. Also, the compressed air supply to such motors typically includes water-oil vapors carried over from the compressor and/or deliberately introduced by means of a lubricator coupled into the air supply line. Vane type air motors especially require oil to be added into the air supply line, so as to aid in sealing, lubricating and cleaning the sliding elements of the motor. Accordingly, the exhausts from a typical pneumatic hoist as above referred to are highly objectionable from the environmental standpoint by reason of their noise outputs as well as by reason of the exhaust oil vapor being pumped into the ambient atmosphere.
The object of the present invention is to provide an improved pneumatic motor powered hoist wherein the motor exhaust acoustic effects are substantially muffled interiorly of the hoist casing which is sealed to the atmosphere except through close clearance load lift means guide apertures permitting ingress and egress of the hoist load carrying means. As the vapor exhausts from the motor expand and cool, they are employed to flow and circulate throughout the entire interior of the hoist casing, thereby simultaneously cooling and lubricating the relatively moving parts of the hoist mechanism. These vapors then exit from the casing through close clearance lift means guide apertures, thereupon further expanding and projecting upon and cooling and lubricating the load carrying chain or cable prior to its running back and forth over the hoist lift wheel.